(i) Field of the Invention
The present invention relates to combustion devices of the type including at least one burner burning a fuel and an oxidant, intended to be placed in a wall of a furnace, as well as to the methods of use of such devices.
(ii) Description of Related Art
Industrial furnaces, traditionally equipped with air-burners burning an air/fuel mixture have recently seen the appearance of oxy-burners, burning a fuel/oxidizer mixture, which are replacing all or some of the conventional air-burners. In the present patent application, xe2x80x9coxidantxe2x80x9d is understood to mean a gas mixture having an oxygen content markedly greater than that of air, such as the mixtures sometimes called xe2x80x9csuperoxygenated airxe2x80x9d, for oxygen contents of between 40 and 70%, or xe2x80x9cimpure oxygenxe2x80x9d for oxygen contents greater than 85%. Generally, the oxy-burner, like these air-burners, is in the form of an individual device with localized fluid ejection, something which frequently causes temperature profile and heat transfer problems in the zone in question by dint of the flame of the oxy-burner.
An object of the present invention is accordingly to provide a novel design of fuel/oxidizer combustion assembly making it possible to limit the flame temperature peaks and the emissions of nitrogen oxides and to ensure excellent heat transfer in a furnace.
In order to meet this object and others, according to one feature of the invention, the combustion assembly comprises at least one pair of burners and an oxidizer lance arranged between the burners of the pair and having a lance axis, and a source of oxidant connected to the burners and to the lance for supplying same.
According to other features of the invention:
the lance is arranged so that the lance axis is located substantially halfway between the burner axes and typically makes an angle with them of less than 10xc2x0;
the distance between two burner axes is between 0.4 and 2 meters, depending on the type of furnace.
The present invention also relates to a furnace, especially a charge melting furnace, including at least one, typically substantially vertical, sidewall comprising at least one combustion assembly as defined hereinabove.
According to other features of the invention:
the burner and lance axes are substantially coplanar;
the angle between the plane of the axes of the combustion assembly mounted in the furnace wall and the horizontal is between xe2x88x9225 and +25xc2x0, typically between xe2x88x9220 and +20xc2x0;
the furnace comprises two opposite sidewalls, each of which comprises at least one combustion assembly, the combustion assemblies in the opposite walls being arranged so as to substantially face each other.
The present invention also relates to a method of using an assembly as defined hereinabove, in which the oxidant, feeding the burners and the lance, includes at least 88%, typically 90 to 95%, of oxygen.
According to other features of the invention:
the burners of the same pair have the same fuel and oxidant flow rates;
the combustion assembly is fed with the oxidizer in excess, corresponding to a molar concentration of oxygen in the dry products of combustion of between 0.5% and 10%;
impulse (mass flow rate multiplied by the velocity) [sic] of the oxidizer emitted by the lance lies between 0.5 and 3 times the impulse [sic] of the oxidant/fuel flux emitted by a burner.
Other features and advantages of the present invention will emerge from the following description of embodiments, this description being given by way of illustration but in no way implying limitation, and being made with the appended drawings in which: